Mathamancy Bracer is a Magic Item, possibly an ArtifactErf-b1-p054, that Parson received in his second Stupid MealErf-b1-p053.
It looks like a sleeve of hard plastic, but has a spot into where Parson's calculator watch can snap.Erf-b1-p054
The bracer instantly and effortlessly does raw calculations necessary to analyze probabilities and predict outcomes of battles - that is, Mathamancy.Erf-b1-p054
The effects of the bracer virtually, when combined with Parson's calculator watch, effectively, but not technically, turn its user into a Mathamancer.
Apparently it is an item of great interest to Mathamancy dependent factionsErf-b1-p060 like CharlescommErf-b1-p103Erf-b1-p105.